O2 stock 1.6 to O2 2.2 - stuck on Dell logo

[Guest grumpy_o_g]

I've been a good boy and patiently waited for O2 to send me the OTA link to the Froyo upgrade. I've backed up and followed their instructions to the letter. When I actually try to install the downloaded upgrade it goes straight into a reboot and hangs at the Dell logo (left it for an hour the first time to check). Removing the battery unfreezes it and it goes back to it's previous 1.6 state. The only non-standard thing is it's rooted by Universal Androot - doesn't seem to want me to unroot it. Any ideas would be greatly appreciated as I don't think I'll get much out of Dell or O2. It's GAUSB1110421-EU build 3883. It shows the new Market format now by the way, despite still being at 1.6.

Thanks all in anticipation.